USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 81
Band Nr. Center Freq. Band Nr. Center Freq. Band Nr. Center Freq.
16 40Hz 26 400Hz 36* 4000Hz
17 50Hz 27* 500Hz 37 5000Hz
18* 63Hz 28 630Hz 38 6300Hz
19 80Hz 29 800Hz 39* 8000Hz
20 100Hz 30* 1000Hz 40 10000Hz
21* 125Hz 31 1250Hz 41 12500Hz
22 160Hz 32 1600Hz 42* 16000Hz
23 200Hz 33* 2000Hz 43 20000Hz
Note: Bands marked with an asterisk (*) are those present in an octave equalizer.
A Feature Unit that supports the Graphic Equalizer Control is not required to implement the full set of
filters. A subset (for example, octave bands) may be implemented. During a Get Control request, the
bmBandsPresent field in the parameter block is a bitmap indicating which bands are effectively
implemented and thus reported back in the returned parameter block. Consequently, the number of bits set
in this field determines the total length of the returned parameter block. During a Set Control request, a
bit set in the bmBandsPresent field indicates there is a new setting for that band in the parameter block
that follows. The new values must be in ascending order. If the number of bits set in the bmBandsPresent
field does not match the number of parameters specified in the following block, the control pipe must
indicate a stall.
A Graphic Equalizer Control can support all possible Control attributes (CUR, MIN, MAX, and RES).
However, if a certain attribute is supported, it must do so for all individual bands. The settings for the
CUR, MIN, and MAX attributes can range from +31.75 dB (0x7F) down to –32.00 dB (0x80) in steps of
0.25 dB (0x01). The settings for the RES attribute can only take positive values and range from 0.25 dB
(0x01) to +31.75 dB (0x7F). The Graphic Equalizer Control honors the request to the best of its abilities.
It may round the bBandxx attribute values to their closest available settings. It will report these settings
when queried during a Get Control request.
Only the first form of the Feature Unit Control request for Graphic Equalizer Control is supported. A
particular Graphic Equalizer Control within a Feature Unit is addressed through the Unit ID and Channel
Number fields of the Set/Get Feature Unit Control request. The valid range for the Channel Number field
is from zero (the ‘master’ channel) up to the number of logical channels in the audio channel cluster.
Table 5-27: Graphic Equalizer Control Parameter Block
Control Selector GRAPHIC_EQUALIZER_CONTROL
wLength 4+(number of bits set in bmBandsPresent : NrBits)
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 82
Offset Field Size Value Description
0 bmBandsPresent 4 Bit Map A bit set indicates the band is present:
D0: Band 14 is present
D1: Band 15 is present
…
D29: Band 43 is present
D30: Reserved
D31: Reserved
4 bBand(Lowest) 1 Number The setting for the attribute of the lowest
band present:
0x7F: +31.75 dB
0x7E: +31.50 dB
…
0x00: 0.00 dB
…
0x82: -31.50 dB
0x81: -31.75 dB
0x80: -32.00 dB
… … … … …
4+(NrBits-1) bBand(Highest) 1 Number The setting for the attribute of the highest
band present.
5.2.2.4.3.7 Automatic Gain Control
The Automatic Gain Control (AGC) is one of the building blocks of a Feature Unit. An Automatic Gain
Control can have only the current setting attribute (CUR). The position of an Automatic Gain Control
CUR attribute can be either TRUE or FALSE.
In the first form of the request, a particular Automatic Gain Control within a Feature Unit is addressed
through the Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid
range for the Channel Number field is from zero (the ‘master’ channel) up to the number of logical
channels in the audio channel cluster.
Table 5-28: First Form of the Automatic Gain Control Parameter Block
Control Selector AUTOMATIC_GAIN_CONTROL
wLength 1
Offset Field Size Value Description
0 bAGC 1 Bool The setting for the attribute of the
addressed Automatic Gain Control. On
when TRUE, off when FALSE.
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for all available AGC Controls in the Feature Unit.
Table 5-29: Second Form of the Automatic Gain Control Parameter Block
Control Selector AUTOMATIC_GAIN_CONTROL
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 83
wLength Number of available Controls: NrAv
Offset Field Size Value Description
0 bAGC(1) 1 Bool The setting for the attribute of the first
Automatic Gain Control.
… … … … …
NrAv-1 bAGC(NrAv) 1 Bool The setting for the attribute of the last
Automatic Gain Control.
5.2.2.4.3.8 Delay Control
The Delay Control is one of the building blocks of a Feature Unit. A Delay Control can support all
possible Control attributes (CUR, MIN, MAX, and RES). The settings for the CUR, MIN, MAX, and RES
attributes can range from zero (0x0000) to 1023.9844ms (0xFFFF) in steps of 1/64 ms or 0.015625 ms
(0x0001). The Delay Control honors the request to the best of its abilities. It may round the wDelay
attribute value to its closest available setting. It will report this rounded setting when queried during a Get
Control request.
In the first form of the request, a particular Delay Control within a Feature Unit is addressed through the
Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid range for the
Channel Number field is from zero (the ‘master’ channel) up to the number of logical channels in the
audio channel cluster.
Table 5-30: First Form of the Delay Control Parameter Block
Control Selector DELAY_CONTROL
wLength 2
Offset Field Size Value Description
0 wDelay 2 Number The setting for the attribute of the
addressed Delay Control:
0x0000: 0.0000 ms
0x0001: 0.0156 ms
0x0002: 0.0312 ms
…
0x0040: 1.0000 ms
…
0xFFFD: 1023.9531 ms
0xFFFE: 1023.9687 ms
0xFFFF 1023.9844 ms
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for all available Delay Controls in the Feature Unit.
Table 5-31: Second Form of the Delay Control Parameter Block
Control Selector DELAY_CONTROL
wLength (Number of available Controls: NrAv)*2
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 84
Offset Field Size Value Description
0 wDelay(1) 1 Number The setting for the attribute of the first
Delay Control.
… … … … …
(NrAv-1)*2 wDelay(NrAv) 1 Number The setting for the attribute of the last
Delay Control.
5.2.2.4.3.9 Bass Boost Control
The Bass Boost Control is one of the building blocks of a Feature Unit. A Bass Boost Control can have
only the current setting attribute (CUR). The position of a Bass Boost Control CUR attribute can be either
TRUE or FALSE.
In the first form of the request, a particular Bass Boost Control within a Feature Unit is addressed through
the Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid range for
the Channel Number field is from zero (the ‘master’ channel) up to the number of logical channels in the
audio channel cluster.
Table 5-32: First Form of the Bass Boost Control Parameter Block
Control Selector BASS_BOOST_CONTROL
wLength 1
Offset Field Size Value Description
0 bBassBoost 1 Bool The setting for the addressed Bass Boost
Control’s CUR attribute. On when TRUE,
off when FALSE.
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for the CUR attribute for all available Bass Boost Controls in the Feature Unit.
Table 5-33: Second Form of the Bass Boost Control Parameter Block
Control Selector BASS_BOOST_CONTROL
wLength Number of available Controls: NrAv
Offset Field Size Value Description
0 bBassBoost(1) 1 Bool The setting for the CUR attribute of the
first Bass Boost Control.
… … … … …
NrAv-1 bBassBoost(NrAv) 1 Bool The setting for the CUR attribute of the
last Bass Boost Control.
5.2.2.4.3.10 Loudness Control
USB Device Class Definition for Audio Devices
Release 1.0 March 18, 1998 85
The Loudness Control is one of the building blocks of a Feature Unit. A Loudness Control can have only
the current setting attribute (CUR). The position of a Loudness Control CUR attribute can be either TRUE
or FALSE.
In the first form of the request, a particular Loudness Control within a Feature Unit is addressed through
the Unit ID and Channel Number fields of the Set/Get Feature Unit Control request. The valid range for
the Channel Number field is from zero (the ‘master’ channel) up to the number of logical channels in the
audio channel cluster.
Table 5-34: First Form of the Loudness Control Parameter Block
Control Selector LOUDNESS_CONTROL
wLength 1
Offset Field Size Value Description
0 bLoudness 1 Bool The setting for the addressed Loudness
Control’s CUR attribute. On when TRUE,
off when FALSE.
In the second form, the Channel Number field is set to 0xFF. The parameter block contains a list of
settings for the CUR attribute for all available Loudness Controls in the Feature Unit.
Table 5-35: Second Form of the Loudness Control Parameter Block
Control Selector LOUDNESS_CONTROL
wLength Number of available Controls: NrAv
Offset Field Size Value Description
0 bLoudness(1) 1 Bool The setting for the CUR attribute of the
first Loudness Control.
… … … … …
NrAv-1 bLoudness(NrAv) 1 Bool The setting for the CUR attribute of the
last Loudness Control.
5.2.2.5 Processing Unit Control Requests
The following sections describe the Set and Get Processing Unit Control requests. They are used to
manipulate the audio Controls within a Processing Unit.
最終更新：2011年05月02日 03:34
